The invention relates to a method for manufacturing an electron gun, in which method a number of electrodes is stacked and secured to a number of insulating support rods by securing means.
The invention also relates to a cathode ray tube having an electron gun for generating an electron beam, the electron gun having a number of electrodes secured to a number of insulating support rods by means of securing means.
The invention also relates to an electron gun for use in a cathode ray tube, the electron gun having a number of electrodes secured to a number of insulating support rods by means of securing means.
Such cathode ray tubes are known and are used in for instance television apparatuses and computer monitors.
Conventional electron guns of cathode ray tubes comprise a number of electrodes, which are positioned one after the other, starting from one cathode (for monochromic cathode ray tubes) or from three cathodes (for colour cathode ray tubes). The electrodes have at their outer circumference securing means secured to electrically insulating support rods. Usually the securing means comprise parts such as protrusions, hooks or brackets which are secured to a number of insulating support rods, for instance by being partly embedded in or attached to a number, usually two, beading rods. The insulating support rods, e.g. beading rods, are usually made of glass and form the back-bone of the electron gun to which the electrodes are attached. In order to attach the electrodes to the beading rods, the electrodes are stacked on each other, for instance in a jig, the beading rods are heated to a temperature at which the glass of the beading rods softens, and the beading rods are pressed against the securing means. Thereby the securing means are at least partly embedded in or attached to the softened material of the beading rods, i.e. secured to the insulating support rods. Thereupon the temperature is lowered, and the material of the rods solidifies, trapping part of the securing means in the beading rods.
Although the conventional design and method for manufacturing have been used with some success, the inventor has realized that the ever higher demands that are placed on the performance of the electron gun and the strive for cost reduction have made the disadvantages of the conventional design ever more relevant. It is very difficult in the conventional design to maintain an accurate positioning of the electrodes with respect to each other. Any change of the positions of the electrodes introduces an error in the position and/or shape of the electron beams on the display screen and/or on the relative positions of the electron beams. Such errors have a detrimental effect on the quality of the image on the display screen. Furthermore the number of parts necessary for the manufacturing of the electron gun increases as the number of electrodes increases. This adds to the cost of manufacturing and furthermore increases the risk that the electron gun comprises a flaw.